On Thu, 2018-05-24 at 15:49 -0500, Eric W. Biederman wrote: > I already nacked this approach because the two cases don't > share a bit of code. When I looked closer it was even crazier. It hasn't been clear what you meant by "the two cases don't share a bit of code". The first attempt called security_kernel_read_file(). As per your comments, kexec_load doesn't load a file. Thinking it was a naming issue the second attempt defined a wrapper named security_kernel_read_blob() for security_kernel_read_file(). Still thinking it was a naming issue, this attempt renamed the security_kernel_read_file() to security_kernel_read_data(). > > The way ima uses this hook and the post_load hook today is a travesty. Instead of having multiple functions, each a bit different, for reading a file from the kernel, kernel_read_file() is a generic implementation with both pre and post security calls. I think the pre and post security kernel_read_file() LSM hooks are quite well thought out. The security_kernel_read_file is called before the kernel reads the file. The security_kernel_post_read_file is called after the kernel reads the file. > The way the security_kernel_file_read and security_kernel_file_post_read > are called today and are used by ima don't make the least little bit of > sense. > > Abusing security_kernel_file_read in the module loader and then abusing > security_kernel_file_post_read in the firmware loader is insane. The > loadpin lsm could not even figure this out and so it failed to work > because of these shenanighans. > > Only implementing kernel_file_read to handle the !file case is pretty > much insane. There is no way this should be expanded to cover kexec > until the code actually makes sense. We need a maintainable kernel. It wasn't implemented *only* for the IMA !file case, but as a generic mechanism. True, IMA is only using the security_kernel_read_file hook for detecting !file, but the security_kernel_post_read_file hook is used for verifying the file's integrity. > Below is where I suggest you start on sorting out these security hooks. > - Adding a security_kernel_arg to catch when you want to allow/deny the > use of an argument to a syscall. What security_kernel_file_read and > security_kernel_file_post_read have been abused for. Assuming we define a new LSM hook named "security_kernel_arg", would we also define a new enumeration or could we still use the existing kernel_read_file_id? > > - Removing ima_file_read because it is completely subsumed by the new > call. The existing IMA function wouldn't be removed, but renamed to whatever the new LSM hook is named. > > - Please note with adding this new hook there is no code shared between > the cases, and the lsm code becomes simpler shorter when it can assume > security_kernel_file_post_read always takes a struct file. (Even with > the addition of a new security hook). We would be defining a new LSM hook, not removing the existing security_kernel_read_file hook, and only renaming the IMA usage of the hook. If defining a new LSM hook named security_kernel_arg makes you happy, I don't have a problem with implementing it. James, Casey, are you Ok with this? Mimi
